Circular is a French wearable technology company that makes the Circular Ring 2, a titanium smart ring worn on a finger. It tracks sleep, recovery, activity and heart related signals without a screen, with results and coaching delivered through the Circular app.

How it works
Optical sensors shine light into the finger to measure pulse, blood oxygen and changes in blood flow. Temperature and motion sensors add information about sleep and activity. Metal contacts can record a short electrical trace of the heart when the wearer starts a reading. The app combines these signals into sleep stages, recovery scores, alerts and trends.

Key considerations
Core features do not require a subscription, although future or advanced services may differ. Battery life changes with the selected tracking mode. Independent reviews have also reported uneven software reliability, and wellness results do not replace clinical heart testing.